Scientists are normally a pretty measured bunch . But in recent months , they 've been resorting to some unusual language to get our attention . One top climatologist recently tweeted : `` If even a small fraction of Arctic sea floor carbon is released to the atmosphere , we 're f 'd . '' When scientists start swearing in public , it is time for everyone to start worrying .

It 's not just the scientists that are raising the alarm . This Sunday , hundreds of thousands of people are taking to the streets around the world in the largest climate mobilization in history . If they were n't listening before , our leaders should tune in now . The voice of global concern for action on climate change is back , and this time it 's no longer an environmental issue , it 's an everybody issue .

And time is short . The world is rushing towards a series of potentially catastrophic feedback loops and tipping points in the climate system , which could see the support system of life itself irrecoverably disrupted . From the release of gigantic amounts of arctic methane gas , to the rapid carbon acidification of our oceans , to apocalyptic flooding , the continued warming of our planet is the greatest challenge our species has faced .

The stakes seem too gargantuan to grasp , but it 's this leap in consciousness that 's required for our survival . Our civilization is built on a fragile , delicately interdependent , and unsustainable relationship with the natural world . We ca n't afford to underestimate the massive footprint that humans have on this planet . One quarter of the carbon dioxide in our atmosphere came from our industries . Our oceans are acidifying 10 times faster than at any point in earth 's history . We are stretching the limits of this world .

But none of this is grounds for despair . The solution to the nightmare of runaway climate change is crystal clear , and beautiful . We need to shift our societies and economies off dirty energy and on to 100 % clean , sustainable energy , within a generation . This goal is entirely achievable . Already , 22 % of the world 's electricity comes from clean energy and the sector is growing fast -- we just need to put our foot on the accelerator .

` I 'm on the front lines of this crisis '

Getting to 100 % clean will require a massive battle against the oil and coal industry and their pocket politicians whose subsidies , profits and influence are all at stake . But this change is possible - we now have the alternative energy technology we need to replace fossil fuels . In May , Denmark published a plan to get to 100 % clean by 2050 , at a cost of less than 20 Euros per Dane per year . Countries as diverse as Norway and Uruguay are already nearly at 100 % clean . Even China , the world 's biggest carbon emitter , is rolling out renewables faster than anywhere else on Earth .

The question is not whether we will make this breakthrough , but whether we do so before it is too late . The clock is ticking , the increase in temperature rising steadily towards the 2 degrees Celsius mark - the red line that both scientists and governments have said poses unacceptable risk of the unthinkable .

And that is why the People 's Climate March is so critical . There is a gap between the speed of action our survival requires and the action our governments are taking . The street is how we close that gap , because politicians will move faster when people move them . Most large-scale social change has been spurred by movements , from ending slavery to giving women the right to vote . Saving ourselves by shifting our societies to 100 % clean energy will require one of the largest , most diverse , and most sustained movements we 've ever seen .

On Sunday , that movement will step forward . A new cast of characters in an unprecedentedly broad coalition and cross section of society will take to the street . Climate change has gone beyond environmentalism , it 's now about the economy , jobs , justice , family , security . It 's about the survival of everything we love .

The UN Climate summit happening two days after the march is an opportunity to build momentum , no more . The Paris summit next year is when we 'll need our leaders to sign a new global agreement . If we learned one thing from the 2009 Copenhagen summit , it 's that one global summit will never be a panacea .

But the thud of peoples boots marching across the planet together with 130 leaders meeting to discuss a collective response to this crisis heralds a fresh momentum for the road ahead . Even before the mobilization has happened , political leaders are responding to it . Some are even joining the march .

In the final analysis , the question is whether we human beings are capable of being wise , farsighted , and unified enough to pass this test of survival . Many civilizations have fallen to the consequences of outstripping their environments . But our civilization is the first truly global one , with the power to end human life . One way or another , we may be the last civilization . For the sake of our children and their children , we must find the hope , wisdom and unity to save it .

READ MORE : On front lines of climate change crisisREAD MORE : Why warming is imminent threat to U.S.

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People 's Climate March takes place Sunday in cities around the world

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Patel : World is rushing towards a series of potentially catastrophic tipping points on climate

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Patel : We need to shift societies off oil and gas energy and onto renewable energy in a generation